Numerous types of labels are known for indicating whether a container has been opened or subjected to tampering. These labels are known as tamper-indicating or tamper-evident labels. Each of these labels has a feature that is altered when the container is opened to indicate that the container has not remained sealed. One such label is simply a strip of paper, or other easily torn material, that bridges a joint between a container's top and the container's body. When the top is removed, the tape is severed. Another tamper-evident label, shown, in U.S. Pat. No. 3,935,960 (Cornell) uses a layer of material that changes color when it is flexed. The layer is placed on the container such that it is necessarily flexed when the container is opened to indicate tampering. Also, U.S. Pat. Nos. 4,121,003 (Williams) and 4,184701 (Franklin) show labels that indicate tampering by providing the label with an adhesive that contains information, parts of the adhesive remaining on both the portion of the label staying on the article and the portion of the label that is detached.
It is also known to use labels that are difficult to produce, such as those having holograms, to authenticate an article. For example, U.S. Pat. No. 4,501,439 (Antes) discloses a hologram attached to an article for authenticating the article, the image generated by the hologram being read only by a specially-designed instrument. U.S. Pat. Nos. 4,921,319; 5,044,707; and 5,085,514 (Mallik) also show authenticating holograms, which allow documents such as passports to be viewed through the hologram.